Equine flu - diagnosis, treatment and prevention

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Equine Influenza ('flu') is probably the main respiratory infection affecting horses. It has a worldwide distribution, and can cause a severe illness in some cases. Fortunately, prevention is possible with current vaccinations. This is a very current topic, with a recent outbreak in Australia between August and October 2007. This continent had previously been unaffected by equine flu, and the outbreak appears to have spread from imported Japanese stallions.


What is Equine Influenza?

This is a severe respiratory viral infection, with a short incubation period of 3-4 days, and a rapid worsening of symptoms. It is particularly likely to spread rapidly in overstocked situations.

The virus is spread by inhalation of water droplets via the nose, and then causes damage to tissues lining the respiratory tract. It can cause death of large areas of the lining tissue or mucosa.


These include high fever, clear nasal discharge, dry cough, and swollen submental lymph nodes (under the jaw). In addition, you may notice that your horse has depression and lethargy, a clear eye discharge, a poor appetite, and a reluctance to drink. There may even be a degree of swelling of the limbs, with a resultant reluctance to move. Occasionally secondary pneumonia can occur, especially in the very old and the very young; this can lead to death.

Causative Agent

The Equine-1 (H7N7) and equine-2 (H3N8); influenza A is a subtype of the latter. Unlike the human influenza virus, which changes every year, equine flu virus has more stable subtypes. Horse flu viruses were only isolated in 1956.

Occasionally carrier status occurs in equines, when an incomplete immune response to infection has occurred and the virus has not been eliminated. Such horses are shedding virus and infectious despite appearing well.

Current Western Treatments

Affected horses need complete rest for at least 6 weeks. It takes one week to recover at best, but 6 weeks for any mucosal damage to be reversed, hence the need for a longer period of rest. During recovery, it is important that any stable used must have good ventilation, with minimal dust levels. Mucolytic agents and antibiotics may be necessary if secondary infection occurs.

Complementary Therapies

Supportive care can help, such as reiki, spiritual healing, crystal healing, acupressure, shiatsu, and aromatics. These can help the horse's immune system and ability to heal itself. The aromatics (animal aromatherapy, whereby the animal chooses remedies on the basis of scent and taste from a selection offered) may have specific effects on resistance to infection and the release of supportive hormones.


Influenza vaccines have been available for many years, and initially only provided protection for a few months. Current improved vaccines protect for 10-15 months. Vaccination is given as a primary course of 2 doses, 3-6 weeks apart, followed by boosters at 6-12 month intervals.

Side effects are rare, and may be due to inflammation at the injection site, occasional allergy, or general poor well-being.

Certification of flu vaccination may be needed for horses that travel or compete

Homeopathic nosodes may be helpful in preventing influenza. Nosodes are created from the equine virus by diluting many times in water. The water then holds the memory of the molecule, which may be enough to stimulate an immune response. There tends to be a lower side effect rate with nosodes, but there is limited evidence of their efficacy.

Dr Alison Grimston is a holistic doctor and animal healer